Apparatus for treating a workpiece with steam and ozone

ABSTRACT

In a method for processing a workpiece to remove material from a first surface of the workpiece, steam is introduced onto the first surface under conditions so that at least some of the steam condenses and forms a liquid boundary layer on the first surface. The condensing steam helps to maintain the first surface of the workpiece at an elevated temperature. Ozone is provided around the workpiece under conditions where the ozone diffuses through the boundary layer and reacts with the material on the first surface. The temperature of the first surface is controlled to maintain condensation of the steam.

This Application is a Continuation of U.S. patent application Ser. No.09/621,028, filed Jul. 21, 2000 and now pending, which is aContinuation-in-Part of U.S. patent application Ser. No. 60/145,350,filed Jul. 23, 1999, and also a Continuation-in-Part of U.S. patentapplication Ser. No. 09/061,318, filed Apr. 16, 1998, now abandoned,which in turn is a Continuation-in-Part of U.S. patent application Ser.No. 08/853,649, filed May 9, 1997, now U.S. Pat. No. 6,240,933. Ser. No.09/621,028 is also a Continuation-in-Part of Ser. No. 08/853,649 and ofInternational Patent Application PCT/US99/08516, filed Apr. 16, 1999,which claims priority to U.S. patent application Ser. Nos. 60/099,067,filed Sep. 3, 1998 and 60/125,304, filed Mar. 19, 1999. PCT/US99/08516is also a Continuation-in-Part of Ser. No. 09/061,318, filed Apr. 16,1998 and now abandoned, which is a Continuation-in-Part of Ser. No.08/853,649. U.S. patent application Ser. No. 09/621,028 is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

The cleaning of semiconductor wafers is often a critical step in thefabrication processes used to manufacture integrated circuits or thelike. The geometries on wafers are often on the order of fractions of amicron, while the film thicknesses may be on the order of 20 Angstroms.This renders the devices highly susceptible to performance degradationdue to organic, particulates or metallic/ionic contamination. Evensilicon dioxide, which is used in the fabrication structure, can beconsidered a contaminant if the quality or thickness of the oxide doesnot meet design parameters.

Although wafer cleaning has a long history, the era of “modern” cleaningtechniques is generally considered to have begun in the early 1970s whenRCA developed a cleaning sequence to address the various types ofcontamination. Although others developed the same or similar processesin the same time frame, the general cleaning sequence in its final formis basically the same.

The first step of the RCA cleaning sequence involves removal of organiccontamination using sulfuric acid and hydrogen peroxide mixtures. Ratiosare typically in the range of 2:1 to 20:1, with temperatures in therange of 90-140 degrees Celsius. This mixture is commonly called“piranha.” A recent enhancement to the removal of organic contaminationreplaces the hydrogen peroxide with ozone that is bubbled or injectedinto the sulfuric acid line.

The second step of the process involves removal of oxide films withwater and HF (49%) in ratios of 200:1 to 10:1, usually at ambienttemperatures. This processing typically leaves regions of the wafer in ahydrophobic condition.

The next step of the process involves the removal of particles and there-oxidation of hydrophobic silicon surfaces using a mixture of water,hydrogen peroxide, and ammonium hydroxide, usually at a temperature ofabout 60-70 degrees Celsius. Historically, ratios of these componentshave been on the order of 5:1:1. In recent years, that ratio has morecommonly become 5:1:0.25, or even more dilute. This mixture is commonlycalled “SC1” (standard clean 1) or RCA1. Alternatively, it is also knownas HUANG1. Although this portion of the process does an outstanding jobof removing particles by simultaneously growing and etching away asilicon dioxide film on the surface of a bare silicon wafer (inconjunction with creating a zeta potential which favors particleremoval), it has the drawback of causing metals, such as iron andaluminum, in solution to deposit on the silicon surface.

In the last portion of the process, metals are removed with a mixture ofwater, hydrogen peroxide, and hydrochloric acid. The removal is usuallyaccomplished at around 60-70 degrees Celsius. Historically, ratios havebeen on the order of 5:1:1, but recent developments have shown that moredilute chemistries are also effective, including dilute mixtures ofwater and HCl. This mixture is commonly referred to as “SC2” (standardclean 2), RCA2, or HUANG2.

The foregoing steps are often run in sequence, constituting what iscalled a “pre-diffusion clean.” Such a pre-diffusion clean insures thatwafers are in a highly clean state prior to thermal operations whichmight incorporate impurities into the device layer or cause them todiffuse in such a manner as to render the device useless. Although thisfour-step cleaning process is considered to be the standard cleaningprocess in the semiconductor industry, there are many variations of theprocess that use the same sub-components. For example, the piranhasolution may be dropped from the process, resulting in a processingsequence of: HF−>SC1−>SC2. In recent years, thin oxides have been causefor concern in device performance, so “hydrochloric acid last”chemistries have been developed. In such instances, one or more of theabove-noted cleaning steps are employed with the final clean includinghydrochloric acid in order to remove the silicon backside from the wafersurface.

The manner in which a specific chemistry is applied to the wafers can beas important as the actual chemistry employed. For example, HF immersionprocesses on bare silicon wafers can be configured to be particleneutral. HF spraying on bare silicon wafers typically shows particleadditions of a few hundred or more for particles at 0.2 microns nominaldiameter.

Although the four-chemistry clean process described above has beeneffective for a number of years, it nevertheless has certaindeficiencies. Such deficiencies include the high cost of chemicals, thelengthy process time required to get wafers through the various cleaningsteps, high consumption of water due to the need for extensive rinsingbetween chemical steps, and high disposal costs. The result has been aneffort to devise alternative cleaning processes that yield results asgood as or better than the existing four-chemistry clean process, butwhich are more economically attractive.

Various chemical processes have been developed in an attempt to replacethe existing four-chemistry process. However, such cleaning processeshave failed to fully address all of the major cleaning concerns of thesemiconductor processing industry. More particularly, they have failedto fully address the problem of minimizing contamination from one ormore of the following contaminants: organics, particles, metals/ions,and silicon dioxide.

Accordingly, there is a need for improved systems and methods forprocessing and cleaning wafers or workpieces.

SUMMARY OF THE INVENTION

In a first aspect, in a method for processing a workpiece to removematerial from a first surface of the workpiece, steam is introduced ontothe first surface under conditions so that at least some of the steamcondenses and forms a liquid boundary layer on the first surface. Thecondensing steam helps to maintain the first surface of the workpiece atan elevated temperature. Ozone is provided around the workpiece underconditions where the ozone diffuses through the boundary layer andreacts with the material on the first surface. The temperature of thefirst surface is controlled to maintain condensation of the steam.

In a second aspect, the temperature of the first surface is controlledvia a heat sink in contact with the workpiece.

In a third aspect, the temperature of the first surface is controlledvia a temperature-controlled stream of liquid delivered to the second orback surface of the workpiece, while steam and ozone are delivered to anenclosed process region and the steam condenses on the first or frontsurface.

In a fourth aspect, the workpiece is rotated while the steam condenses.

In a fifth aspect, additives, such as hydrofluoric acid, ammoniumhydroxide or other chemicals may be added to promote cleaning.

The methods of the invention allow for use of high temperatures whichare advantageous is speeding up the reaction times for removing organicor other materials from the surface of the workpiece. The methods of theinvention also have the potential for removing of difficult to removematerials, which may require more energy for removal than can be readilyprovided using only hot water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of one embodiment of an apparatusfor treating a semiconductor workpiece in which ozone is injected into aline containing a pressurized treatment liquid.

FIG. 2 is a schematic block diagram of one embodiment of an apparatusfor treating a semiconductor workpiece in which the semiconductorworkpiece is indirectly heated by heating a treatment liquid that issprayed on the surface of the workpiece.

FIG. 3 is a flow diagram illustrating one embodiment of a process flowfor treating a semiconductor workpiece with a treatment fluid and ozone.

FIG. 4 is a schematic block diagram of an alternative embodiment of thesystem set forth in FIG. 2 wherein the ozone and treatment fluid areprovided to the semiconductor workpiece along different flow paths.

FIG. 5 is a schematic block diagram of an embodiment of an apparatus fortreating a semiconductor workpiece in which pressurized steam and ozoneare provided in a pressurized chamber containing a semiconductorworkpiece.

FIG. 6 is a schematic block diagram of an embodiment of an apparatus fortreating a semiconductor workpiece in which an ultra-violet lamp is usedto enhance the kinetic reactions at the surface of the workpiece.

FIG. 7 is a schematic block diagram of an embodiment of an apparatus fortreating a semiconductor workpiece in which liquid gas contactors areused to enhance the kinetic reactions at the surface of the workpiece.

DETAILED DESCRIPTION OF THE INVENTION

A novel chemistry, application technique, and system is used to reducethe contamination and speed up processing in the manufacturing ofsemiconductor wafers, memory disks, photomasks, optical media, and othersubstrates (collectively referred to here as “wafers”) requiring a highlevel of clean. Contamination may occur from organics, particles,metal/ions, and silicon dioxide. Cleaning of wafers is achieved bydelivery of a chemical stream to the workpiece surface. Ozone isdelivered either into the liquid process stream or into the processenvironment. The chemical stream, which may be in the form of a liquidor vapor, is applied to the wafer in a system which allows for controlof the liquid boundary layer thickness. The chemical stream may includeammonium hydroxide for simultaneous particle and organic removal,another chemical to raise the pH of the solution, or other chemicaladditives designed to accomplish one or more specific cleaning steps.

Wafers are preferably placed in a standard Teflon wafer cassette, or ina centrifugal process chamber utilizing a “carrierless” rotor design.During processing, the wafers and/or cassette are preferably rotated inthe chamber.

A processing solution is preferably heated and sprayed onto the wafersurface. This heats the surface of the wafer as well as the environment.If the spray is shut off, a thin liquid film remains on the wafersurfaces. However, preferably the liquid spray is continued for theduration of the chemical process step. If the wafer surface ishydrophobic, a surfactant may be added to the liquid chemical to createa thin film of liquid on the surfaces. The boundary layer of theprocessing solution at the wafer surface is advantageously controlledthrough the use of the rotation rate, the flow rate of the processingsolution, and/or the injection technique (nozzle design) used to deliverthe liquid (or steam) stream to the surfaces of the wafers.

Ozone is concurrently injected into the enclosed chamber during theliquid spray, either through the same manifold as the liquid delivery orthrough a separate manifold. Ozone injection may continue after thespray has shut off. If the wafer surfaces begin to dry (as in the caseof a non-continuous spray), a brief spray may be used to replenish theliquid. This insures that the exposed wafer surfaces remain wetted atall times and that the elevated temperature at the wafer surfaces isalso maintained. The process may also be used on a single wafer, ratherthan on an entire batch.

While ozone has a limited solubility in the hot liquid solution, it isstill able to diffuse through the solution and react with the surface ofthe wafer (whether it is silicon, photoresist, etc.) at the liquid/solidinterface. Thus diffusion, rather than dissolution, is the primarymechanism used to deliver ozone to the surfaces of the wafers. Waterapparently helps to hydrolyze carbon-carbon bonds or accelerate theoxidation of silicon surfaces by hydrolyzing silicon-hydrogen orsilicon-hydroxyl bonds. The elevated temperature promotes the reactionkinetics and the high concentration of ozone in the gas phase promotesdiffusion of the ozone through the liquid film, even though theincreased temperature of the liquid film does not result in a solutionhaving a high concentration of ozone dissolved in it.

The flow of ozone can be delivered to the process chamber through avapor generator or the like. Such a generator is filled with water,which is temperature controlled. Thus the ozone gas stream is enrichedwith water vapor which maintains the boundary layer on each wafersurface at a minimal thickness so that the layer does not inhibitdiffusion. At the same time, such delivery assists in preventing thewafers from drying completely during the process.

A high capacity ozone generator is preferably used to produce a mixedeffluent containing a high concentration of ozone in combination with ahigh flow rate. A higher concentration of ozone increases the quantityof ozone provided to the surface of the wafer. A higher flow rateincreases the rate at which fresh reactants are replenished, and spentor exhausted reactants are carried away from the wafer.

Purely maximizing the concentration of ozone is not optimal for processperformance, as the amount of ozone then generated is then too small tocreate an adequate concentration within the process chamber. On theother hand, simply maximizing flow rate or volume, without sufficientconcentration will result in rapid depletion of ozone in the processchamber (as the ozone will react rapidly with organic materials in theprocess chamber). Thus, both high concentration and high flow rates areneeded.

In known spray processing operations, wafer rotational speeds are in therange of 10-100 rpm. Such low speeds tend to allow a thick boundarylayer of liquid to build up on the surfaces of the wafers to create adiffusion barrier, which, in turn, inhibits the reaction rate. It hasbeen found, however, that a continuous spray of liquid, such as thede-ionized water that is heated to maintain the surface temperature ofthe wafers, combined with high rotational speeds (>300 rpm), generates avery thin boundary layer that minimizes the diffusion layer thicknessthereby leading to an enhanced stripping rate. It has also been foundthat increases in the rotational rate of the wafers during processingresults in a corresponding increase in the strip rate. For example, anincrease in the rotational rate from 300 to 800 rpm results in the striprate increasing by a factor of 2 or more. A further increase to 1500 rpmhas been seen to result in another two-fold increase. Rotation rates ofup to 3000 rpm are anticipated.

To further enhance the process, the temperature of the liquid supply(water supply) can be heated to generate a supply of saturated steamunder pressure to the process chamber. Under such circumstances, it ispossible to achieve wafer surface temperatures in excess of 100 degreesCelsius, thereby further accelerating the reaction kinetics. A steamgenerator may be used to pressurize the process chamber to achieve thedesired temperatures. For example, saturated steam at 126 degreesCelsius may be used with a corresponding increase in the pressure of theprocess chamber to 240 K Pa (35 psia). The increased pressure within theprocessing chamber also provides for use of higher ozone concentrations,thereby generating a higher diffusion gradient across the boundary layerat the surface of each wafer. Still further, the use of steam alsoallows for the use of lower rotation rates to achieve the requisite thinboundary layers at the surfaces of the wafers. The oxidation rate of theozone may also be enhanced by irradiating the surfaces of the waferswith ultra-violet light.

The invention allows particles, metals, and organics to be removed in asingle processing step. Further, it is now possible to regenerate afresh, clean, controlled chemical oxide film in that same step. To thisend, certain additives may be provided in the processing liquid tospecifically target certain contaminants and/or to enhance theeffectiveness of the overall process. For example, ammonium hydroxidemay be added to the processing liquid (e.g., deionized water) to reduceparticle counts on the workpieces. In such a process, the ozone preventspitting of the silicon surface by the ammonium hydroxide.

Other additives that enhance the cleaning capability of the overallprocess include HF and HCl. Such additives have the followingbenefits/effects: 1) removal of organic contaminants; 2) removal ofoxide and regeneration of a controlled chemical oxide; 3) removal ofparticles; 4) removal of metals.

After one or more of the foregoing cleaning process steps has beencompleted, the wafers are prepared for subsequent cleaning steps. Thewafers are preferably rinsed with deionized water or a suitable aqueoussolution. At this time, the ozone within the processing chamber may alsobe purged with, for example, a nitrogen flush.

If an additive that enhances the metal removal capabilities of thesolution is not used, it may be desirable to execute a furtherprocessing step for metal removal. In one or more such cleaning steps,metal and/or silicon dioxide may be removed from the surfaces of thewafers by applying a temperature controlled mixture containinghydrofluoric acid and/or hydrochloric acid, chloroacetic acid, or otherhalogenated chemistry. Ozone may or may not be introduced into theliquid stream or the process environment during this step.

After one or more of the foregoing steps have been completed, includingany intermediate cleaning steps, the wafers are subject to a finalrinsing in deionized water or an aqueous solution. After the rinse, thewafers may be dried in a manner that may include the use of heatednitrogen, another inert gas flow, or organic vapors. Additionally, thewafers may be rotated during the drying process.

The disclosed process is applicable to various manufacturing steps thatrequire cleaning or selective removal of contaminants from the surfaceof a workpiece. For example, one or more of the steps may be used toremove photoresist from the surface of a semiconductor wafer. A layer ofphotoresist and a corresponding layer of an anti-reflective coating(ARC) may be removed in a single processing step using a singleprocessing solution. An aqueous solution having a high pH, such as asolution of ammonium hydroxide and/or tetra-methyl ammonium hydroxideand deionized water, may be used to form a controlled boundary layerthat cooperate with ozone to remove both the photoresist and theanti-reflective coating.

Novel aspects include:

1) The use of a temperature controlled liquid chemical source deliveredto the wafer surface to stabilize the temperature of the wafer and,depending on the liquid utilized, provide a supply of water to supporthydrolysis of the carbon-carbon bonds of contaminants at the surface ofeach wafer.

2) The control of the thickness of the boundary layer of liquid presenton the wafer surface so that it is not of sufficient thickness tosignificantly inhibit the diffusion of ozone to the wafer surface. Assuch, the ozone is allowed to diffuse through the controlled boundarylayer, where it can oxidize silicon, organics, or metals at the surface,or otherwise support any desired reaction. The boundary layer may becontrolled through the control of wafer rotation rate, vapor delivery,controlled liquid spray, the use of steam, the use of surfactants or acombination of more than one of these techniques.

3) The process takes place in an enclosed processing chamber, which mayor may not be used to produce a pressurized processing environment.

4) The process utilizes a mixed effluent having a higher concentrationof ozone in combination with a higher flow rate for increasing the rateat which fresh reactants are supplied to the surface of the wafer.

The invention resides as well in sub-combinations of the methods andapparatus

Apparatus for supplying a mixture of a treatment liquid and ozone fortreatment of a surface of a workpiece, such as a semiconductorworkpiece, to execute the foregoing processes are set forth below. Thepreferred embodiment of the apparatus comprises a liquid supply linethat is used to provide fluid communication between a reservoircontaining the treatment liquid and a treatment chamber housing thesemiconductor workpiece. A heater heats the workpiece, either directlyor indirectly. Preferably, the workpiece is heated by heating thetreatment liquid that is supplied to the workpiece. One or more nozzlesaccept the treatment liquid from the liquid supply line and spray itonto the surface of the workpiece while an ozone generator providesozone into an environment containing the workpiece.

Referring to FIG. 1, the treatment system, shown generally at 10,includes a treatment chamber 15 that contains one or more workpieces 20,such as semiconductor wafer workpieces. Although the illustrated systemis directed to a batch workpiece apparatus, it is readily adaptable foruse in single workpiece processing as well.

The semiconductor workpieces 20 are preferably supported within thechamber 15 by one or more supports 25 extending from, for example, arotor assembly 30. Rotor assembly 30 may seal with the housing of thetreatment chamber 15 to form a sealed, closed processing environment.Further, rotor assembly 30 is provided so that the semiconductorworkpieces 20 may be spun about axis 35 during or after treatment withthe ozone and treatment liquid.

The chamber 15 has a volume which is minimized, and is as small aspermitted by design considerations for any given capacity (i.e., thenumber and size of the substrates to be treated). The chamber 15 ispreferably cylindrical for processing multiple wafers in a batch, or aflatter disk-shaped chamber may be used for single wafer processing.Typically, the chamber volume will range from about 5 liters, (for asingle wafer) to about 50 liters (for a 50 wafer system).

One or more nozzles 40 are disposed within the treatment chamber 15 todirect a spray mixture of ozone and treatment liquid onto the surfacesof the semiconductor workpieces 20 that are to be treated. In theillustrated embodiment, the nozzles 40 direct a spray of treatment fluidto the underside of the semiconductor workpieces 20. However, the fluidspray may be directed alternatively, or in addition, to the uppersurface of the semiconductor workpieces 20. The fluid may also beapplied in other ways besides spraying, such as flouring, bulkdeposition, immersion, etc.

Treatment liquid and ozone are preferably supplied to the nozzles 40 bysystem components uniquely arranged to provide a single fluid linecomprising ozone mixed with the treating liquid. A reservoir 45 definesa chamber 50 in which the liquid that is to be mixed with the ozone isstored. The chamber 50 is in fluid communication with, or connected to,the input of a pump mechanism 55. The pump mechanism 55 provides theliquid under pressure along a fluid flow path, shown generally at 60,for ultimate supply to the input of the nozzles 40. The preferredtreatment fluid is deionized water. Other treatment fluids, such asother aqueous or non-aqueous solutions, may also be used.

Fluid flow path 60 may include a filter 65 to filter out microscopiccontaminants from the treatment fluid. The treatment fluid, still underpressure, is provided at the output of the filter 65 (if used) alongfluid flow line 70. Ozone is injected along fluid flow line 70. Theozone is generated by ozone generator 75 and is supplied along fluidflow line 80 under pressure to fluid flow line 70. Optionally, thetreatment liquid, now injected with ozone, is supplied to the input of amixer 90 that mixes the ozone and the treatment liquid. The mixer 90 maybe static or active. From the mixer 90, the treatment liquid and ozoneare provided to be input of nozzles 40 which, in turn, spray the liquidon the surface of the semiconductor workpieces 20 that are to be treatedand, further, introduce the ozone into the environment of the treatmentchamber 15.

To further concentrate the ozone in the treatment liquid, an output ofthe ozone generator 75 may be supplied to a dispersion unit 95 disposedin the liquid chamber 50 of the reservoir 45. The dispersion unit 95provides a dispersed flow of ozone through the treatment liquid tothereby add ozone to the fluid stream prior to injection of a furtheramount of ozone along the fluid path 60.

In the embodiment of the system of FIG. 1, spent liquid in chamber 15 isprovided along fluid line 105 to, for example, a valve mechanism 110.The valve mechanism 110 may be operated to provide the spent liquid toeither a drain output 115 or back to the liquid chamber 50 of thereservoir 45. Repeated cycling of the treatment liquid through thesystem and back to the reservoir 45 assists in elevating the ozoneconcentration in the liquid through repeated ozone injection and/orozone dispersion.

The ozone generator 75 is preferably a high capacity ozone generator.One example of a high capacity ozone generator is the ASTeX 8403 OzoneGenerator, manufactured by Applied Science and Technology, Inc., Woburn,Mass., U.S.A. The ASTeX 8403 has an ozone production rating of 160 gramsper hour. At this rate a flow of approximately 12 liters/minute andhaving a concentration of 19% ozone, by weight, can be supported.Another example of a suitable high capacity ozone generator is theSumitomo GR-RL Ozone Generator, manufactured by Sumitomo PrecisionProducts Co., Ltd., Hyogo, Japan which has an ozone production rating of180 g/hr. The ozone generator 75 preferably has a capacity of at least90 or 100 grams per hour, or 110 or 120 grams per hour, with thecapacity more preferably of at least 135 grams per hour. In terms offlow rate and concentration, the capacity should be at least 10 litersper minute at 12%, 13%, 14%, 15% (or higher) concentration by weight.Lower flow rate applications, such as with single wafer processing, mayhave higher concentrations of e.g., 16-19 or greater.

Use of a high capacity ozone generator is especially useful inconnection with the methods and apparatus of the present application,because the present methods and apparatus provide for the delivery ofozone independent of the processing fluid.

In previous methods the ozone was dissolved into the aqueous solution inorder to make it available for the oxidation process on the surface ofthe semiconductor wafer. This limited the amount of ozone, which couldbe delivered to the surface of the semiconductor wafer, to the amount ofozone which could be dissolved into the processing fluid.Correspondingly, there was no incentive to use higher capacity ozonegenerators, because any excess ozone produced would not be absorbed bythe process fluid, and would eventually dissipate and be lost.

FIG. 1, (as well as the other Figures) illustrates various componentsand connections. While showing preferred designs, the drawings includeelements which may or may not be essential to the invention. Theelements essential to the invention are set forth in the claims. Thedrawings show both essential and non-essential elements.

A further embodiment of a system for delivering a fluid mixture fortreating the surface of a semiconductor workpiece is illustrated in FIG.2. Although the system 120 of FIG. 2 appears to be substantially similarto the system 10 of FIG. 1, there are significant differences. Thesystem 120 of FIG. 2 is based in part on the concept that the heating ofthe surfaces of the semiconductor workpieces 20 with a heated liquidthat is supplied along with a flow of ozone that creates an ozonatedatmosphere is highly effective in photoresist stripping, ash removal,and/or cleaning processes. The system 120 therefore preferably includesone or more heaters 125 that are used to heat the treatment liquid sothat it is supplied to the surfaces of the semiconductor workpieces atan elevated temperature that accelerates the surface reactions. It isalso possible to directly heat the workpieces to stimulate thereactions. Such heating may take place in addition to or instead of theindirect heating of the workpieces through contact with the heatedtreatment liquid. For example, supports 25 may include heating elementsthat may be used to heat the workpieces 20. The chamber 15 may include aheater for elevating the temperature of the chamber environment andworkpieces.

The preferred treatment liquid is deionized water, since it appears tobe required to initiate the cleaning/removal reactions at the workpiecesurface, apparently through hydrolysis of the carbon-carbon bonds oforganic molecules. However, significant amounts of water can form acontinuous film on the semiconductor workpiece surface. This film actsas a diffusion barrier to the ozone, thereby inhibiting reaction rates.The boundary layer thickness is controlled by controlling the rpm of thesemiconductor workpiece, vapor delivery, and controlled spraying of thetreatment liquid, or a combination of one or more of these techniques.By reducing the boundary layer thickness, the ozone is allowed todiffuse to the surface of the workpieces and react with the organicmaterials that are to be removed.

FIG. 3 illustrates one embodiment of a process that may be implementedin the system of FIG. 2 when the system 120 is used, for example, tostrip photoresist from the surfaces of semiconductor workpieces. At step200, the workpieces 20 that are to be stripped are placed in, forexample, a Teflon wafer cassette. This cassette is placed in a closedenvironment, such as in chamber 15. Chamber 15 and its correspondingcomponents may be constructed based on a well known spray solvent systemor spray acid such as those available from Semitool, Inc., of Kalispell,Mont., U.S.A. Alternatively, the semiconductor workpieces 20 may bedisposed in chamber 15 in a carrierless manner, with an automatedprocessing system, such as described in U.S. Pat. No. 5,784,797.

At step 205, heated deionized water is sprayed onto the surfaces of thesemiconductor workpieces 20. The heated deionized water heats thesurfaces of the semiconductor workpieces 20 as well as the enclosedenvironment of the chamber 15. When the spray is discontinued, a thinliquid film remains on the workpiece surfaces. If the surface ishydrophobic, a surfactant may be added to the deionized water to assistin creating a thin liquid boundary layer on the workpiece surfaces. Thesurfactant may be used in connection with hydrophilic surfaces as well.Corrosion inhibitors may also be used with the aqueous ozone, thinboundary layer process.

The surface boundary layer of deionized water is controlled at step 210using one or more techniques. For example, the semiconductor workpieces20 may be rotated about axis 35 by rotor 30 to thereby generatecentripetal accelerations that thin the boundary layer. The flow rate ofthe deionized water may also be used to control the thickness of thesurface boundary layer. Lowering of the flow rate results in decreasedboundary layer thickness. Still further, the manner in which thedeionized water is injected into the chamber 15 may be used to controlthe boundary layer thickness. Nozzles 40 may be designed to provide thedeionized water as micro-droplets thereby resulting in a thin boundarylayer.

At step 215, ozone is injected into the fluid flow path 60 during thewater spray, or otherwise provided to the internal chamber environmentof chamber 15. If the apparatus of FIG. 2 is utilized, the injection ofthe ozone continues after the spray has shut off. If the workpiecesurface begins to dry, a brief spray is preferably activated toreplenish the liquid film on the workpiece surface. This ensures thatthe exposed workpiece surfaces remain wetted at all times and, further,ensures that the workpiece temperature is and remains elevated at thedesired reaction temperature. It has been found that a continuous sprayof deionized water having a flow rate that is sufficient to maintain theworkpiece surfaces at an elevated temperature, and high rotationalspeeds (i.e., >300 rpm, between 300 and 800 rpm, or even as high as orgreater than 1500 rpm) generates a very thin boundary layer whichminimizes the ozone diffusion barrier and thereby leads to an enhancedphotoresist stripping rate. As such, the control of the boundary layerthickness is used to regulate the diffusion of reactive ozone to thesurface of the wafer.

The surface layer thickness may range from a few molecular layers (e.g.,about 1 micron), up to 100 microns, (typically 50-100 microns), orgreater.

While ozone has a limited solubility in the heated deionized water, theozone is able to diffuse through the water and react with photoresist atthe liquid/resist interface. It is believed that the presence of thedeionized water itself further assists in the reactions by hydrolyzingthe carbon-carbon bonds of organic deposits, such as photoresist, on thesurface of the wafer. The higher temperature promotes the reactionkinetics while the high concentration of ozone in the gas phase promotesdiffusion of ozone through the boundary layer film even though the hightemperature of the boundary layer film does not actually have a highconcentration of dissolved ozone.

Elevated or higher temperatures means temperatures above ambient or roomtemperature, that is temperatures above 20 or 25° and up to about 200°C.

Preferred temperature ranges are 25-150°, more preferably 55-120° or75-115° C., and still more preferably 85-105° C. In the methodsdescribed, temperatures of 90-100° C., and preferably centering around95° C. may be used.

After the semiconductor workpieces 20 have been processed through thereactions of the ozone and/or liquid with the materials to the removed,the workpieces are subject to a rinse at 220 and are dried at step 225.For example, the workpieces may be sprayed with a flow of deionizedwater during the rinse at step 220. They may then be subject to any oneor more known drying techniques thereafter at step 225.

In the described processes, elevated temperatures are used to acceleratethe reaction rates at the wafer surface. One manner in which the surfacetemperature of the wafer may be maximized is to maintain a constantdelivery of heated processing liquid, such as water or steam, during theprocess. The heated processing liquid contacts and heats the waferduring processing. However, such a constant delivery may result insignificant waste of the water or other processing liquid. In order toconserve water and achieve the thinnest possible boundary layer, a“pulsed flow” of liquid or steam may be used. In instances in which sucha “pulsed flow” fails to maintain the requisite elevated wafer surfacetemperatures, an alternative manner of maintaining the wafer surfacetemperature may be needed. One such alternative is the use of a “hotwall” reactor that maintains the wafer surface and processingenvironment temperatures at the desired level. To this end, the processchamber may be heated by, for example, one or more embedded heatedrecirculating coils, a heating blanket, irradiation from a thermalsource (e.g., and infrared lamp), etc.

In laboratory experiments, a 150 mm silicon wafer coated with 1 micronof photoresist was stripped in accordance with the teachings of theforegoing process. The processing chamber was pre-heated by sprayingdeionized water that was heated to 95 degrees Celsius into theprocessing chamber for 10 minutes. During the cleaning process, a pulsedflow of deionized water heated to 95 degrees Celsius was used. Thepulsed flow included an “on time” of approximately five seconds followedby an “off time” of 10 seconds. The wafer was rotated at 800 rpm and thepulsed flow of deionized water was sprayed into the processing chamberthrough nine nozzles at a rate of 3 liters per minute. Ozone wasinjected into the processing chamber through a separate manifold at arate of 8 liters per minute at a concentration of 12 percent. Theresultant strip rate was 7234 Angstroms/min.

At a higher ozone flow rate, made possible by using a high capacityozone generator for injecting ozone into the processing chamber at arate of 12 liters per minute and having a concentration of 19 percent,the resultant strip rates can be further increased to in excess of 8800Angstroms/minute.

There are many benefits resulting from the use of the semiconductorcleaning processes described above. One of the most significant benefitsis that the conventional 4-chem clean process may be reduced to atwo-chemical step process while retaining the ability to removeorganics, remove particulates, reduce metals and remove silicon dioxide.Process times, chemical consumption, water consumption and wastegeneration are all also significantly reduced. A further benefit of theforegoing process is its applicability to both FEOL and BEOL wafers andstrip processes. Laboratory tests indicate that there is no attack onmetals such as aluminum, titanium, tungsten, etc. A known exception iscopper, which forms a copper oxide in the presence of ozone. This oxideis not a “hard” and uniform passivation oxide, such as the oxide thatforms on metals like aluminum. As a result, the oxide can be readilyremoved.

A still further benefit is the higher ozone flow rates andconcentrations can be used to produce higher strip rates under variousprocessing conditions including lower wafer rotational speeds andreduced temperatures. Use of lower temperatures (between 25 and 75° C.and preferably from 25-65° C. (rather than at e.g., 95° C. as describedabove) may be useful where higher temperatures are undesirable.

One example where this is beneficial is the use of the process with BEOLwafers, wherein metal corrosion may occur if the metal films are exposedto high temperature de-ionized water. Correspondingly, processing atambient temperatures may be preferred. The gain in strip rates notrealized, as a result of not using higher temperatures, is offset byincreases in strip rate due to the increased ozone flow rates andconcentrations. The use of higher ozone concentration can offset theloss of kinetic energy from using lower temperatures.

With reference again to FIG. 3, it will be recognized that process steps205-215 may be executed in a substantially concurrent manner.Additionally, it will be recognized that process steps 205-215 may besequentially repeated using different processing liquids. In suchinstances, each of the processing liquids that are used may bespecifically tailored to remove a respective set of contaminants.Preferably, however, it is desirable to use as few different processingliquids as possible. By reducing the number of different processingliquids utilized, the overall cleaning process is simplified andreducing the number of different processing liquids utilized minimizeschemical consumption.

A single processing liquid may be used to remove organic contaminants,metals, and particles in a single cycle of process steps 205-215. Theprocessing liquid is comprised of a solution of deionized water and oneor more compounds, such as HF or HCl, so as to form an acidic processingliquid solution.

The use of a hydrofluoric acid solution in the process steps set forthat 205-215 provides numerous advantages, including the following:

1. Removal of organic contaminants—The oxidation capability of theprocess has been demonstrated repeatedly on photoresist. Strip ratesoften exceed 8800 A/minute. Considering the fact that in cleaningapplications, organic contamination is generally on the molecular level,the disclosed process has ample oxidation capacity.

2. Removal of oxide and regeneration of a controlled chemicaloxide—Depending on the temperature of the solution and the concentrationof HF in solution, a specific etch rate may be defined. However, theozone will diffuse through the controlled boundary layer and regeneratethe oxide to prevent the wafer from becoming hydrophobic. A 500:1 H₂O:HFmixture at 65 degrees C. will etch SiO₂ at a rate of about 6 A/minute.The same solution at 25 degrees C. will etch SiO₂ at about 2 A/minute. Atypical “native” oxide is generally self limiting at a thickness of 8-12A, which is generally the targeted thickness for the oxide removal.

3. Removal of particles—Although the acidic solutions do not have thefavorable zeta potential present in the SC1 clean noted above, particleremoval in the disclosed process with an HF processing liquid has stillbeen shown to be significant, as it uses the same removal mechanism ofetching and regenerating the oxide surface.

4. Removal of metals—In laboratory experiments, wafers wereintentionally contaminated with iron, nickel and copper. The disclosedprocess with an HF containing processing liquid showed a reduction inmetals of over three orders of magnitude. As an added enhancement, HClcan be used in place of the HF to accomplish the metals removal,although this does not have the same degree of oxide and particleremoval capability. The combination of HF and HCl is a further benefit,as each of these chemistries has significant metals removal capability,but the regeneration of the oxide surface in conjunction with theconversion of metals to metallic oxides and the symbiotic interaction ofthe two acid halides creates an exceptionally favorable environment formetal removal.

An oxide-free (hydrophobic) surface may be generated, if desired, byusing a final HF step in an immersion cell or by use of an HF vapor stepafter the metals removal.

With the use of HF and ozone, the boundary layer is preferablymaintained thick enough to achieve good etch uniformity, by selectingflow rates of liquid onto the workpiece surface, and removal rates ofliquid from the workpiece surface. The boundary layer of the liquid onthe workpiece surface is preferably maintained thick enough so that theetch uniformity is on the order of less than 5%, and preferably lessthan 3% or 2% (3-sigma divided by the mean).

In the HF and ozone process, the ozone concentration is preferably about3-35% or 10-20% by weight (in oxygen). The ozone concentration islargely dependent on the etch rate of the aqueous HF solution used. Whenprocessing silicon, it is desirable that the silicon surface not beallowed to go hydrophobic, indicating the complete etching of thepassivating silicon dioxide surface. HF concentration used is typically0.001 to 10% or 0.01 to 1.0% (by weight). In general, the lowerconcentrations are preferred, with a concentration of about 0.1%providing very good cleaning performance (with an etch rate of 8 A ofthermal oxide per minute at 95C.). The HF solution may includehydrochloric acid to enhance metal removal capability. If used, the HCltypically has a range of concentrations similar to the ranges describedabove for HF.

In the HF and ozone process, a temperature range from 0° C. up to 100°C. may be used. Higher temperatures may be used if the process isconducted under pressure. Particle removal capability of this process isenhanced at elevated temperatures. At ambient temperature, the particleremoval efficiency of dried silicon dioxide slurry particles withstarting counts of around 60,000 particles larger than 0.15 microns, wasabout 95%. At 65° C., this efficiency increased to 99%. At 95° C., theefficiency increased to 99.7%. Although this may appear to be a slightimprovement, the difference in final particle count went from 3000 to300 to about 100 particles, which can be very significant in themanufacture of semiconductor devices.

The HF and ozone process may be included as part of a cleaning sequence,for example: 3:00 (minutes) of HF/O3>3:00 SC1>3:00 HF/O3. In thissequence, the cleaning efficiency increased to over 99.9%. In contrast,the SC1 alone had a cleaning efficiency of only 50% or less. Similarresults have been achieved when cleaning silicon nitride particles aswell.

The steps and parameters described above for the ozone processes applyas well to the ozone with HF and ozone process. These processes may becarried out on batches of workpieces in apparatus such as described inU.S. Pat. No. 5,544,421, or on individual workpieces in an apparatussuch as described in PCT/US99/05676.

Typical chemical application times are in the range of 1:00 to 5:00.Compared to a 4-chem clean process time of around 20:00, the disclosedprocess with an HF and/or HCl containing processing liquid becomes veryattractive. Typical H₂O:HF:HCl concentration ratios are on the order of500:1:1 to 50:1:1, with and without HF and/or HCl. Higher concentrationsare possible, but the economic benefits are diminished. It is importantto note that gaseous HF or HCl could be injected into water to createthe desired cleaning chemistry as well. Due to differences in processorconfigurations and desired cleaning requirements, definition of specificcleaning process parameters will vary based on these differences andrequirements.

The process benefits include the following:

1. Reduction in the amount and types of chemicals used in the cleaningprocess.

2. Reduction in water consumption by the elimination of the numerousintermediate rinse steps required.

3. Reduction in process time.

4. Simplification of process hardware.

The disclosed processes are counter-intuitive. Efforts have been madefor a number of years to replace hydrogen peroxide with ozone inchemistries such as SC1 and, to a lesser degree, SC2. These efforts havelargely failed because they have not controlled the boundary layer andhave not introduced the ozone in such a manner that diffusion throughthe boundary layer is the controlling mechanism instead of dissolutioninto the boundary layer. While the cleaning efficiency of conventionalsolutions is greatly enhanced by increasing temperature, it isrecognized that the solubility of ozone in a given liquid solution isinversely proportional to the temperature of the solution. Thesolubility of ozone in water at 1 degrees Celsius is approximately 100ppm. At 60 degrees Celsius, this solubility drops to less than 5 ppm. Atelevated temperatures, the ozone concentration is thus insufficient topassivate (oxidize) a silicon wafer surface quickly enough to ensurethat pitting of the silicon surface will not occur. Thus the twomechanisms are in conflict with one another when attempting to optimizeprocess performance.

Tests have demonstrated that by applying the boundary layer controltechniques explained in connection with the presently disclosedprocesses, it is possible to process silicon wafers using a 4:1water:ammonium hydroxide solution at 95 C and experience an increasesurface roughness (RMS) of less than 2 angstroms. When this samesolution is applied in an immersion system or in a conventional spraysystem, RMS surface roughness as measured by atomic force microscopyincreases by more than 20 angstroms and the maximum surface roughnessexceeds 190 angstroms. Additionally, while a conventional process willpit the surface to such a degree as to render the surface unreadable bya light-scattering particle counter, the boundary controlled techniquehas actually shown particle reductions of up to 50% on the wafersurface.

In the case of oxidizing and removing organic contamination,conventional aqueous ozone processes show a strip rate on photoresist (ahydrocarbon film) of around 200-700 angstroms per minute. In theboundary layer controlled system of the disclosed processes, the rate isaccelerated to 2500 to 8800. angstroms per minute in a spray controlledboundary layer, or higher when the boundary layer is generated andcontrolled using steam at 15 psi and 126 degrees C.

The disclosed processes are suitable for use in a wide range ofmicroelectronic fabrication applications. One issue which is of concernin the manufacture of semiconductor devices is reflective notching. Inorder to expose a pattern on a semiconductor wafer, the wafer is coatedwith a photo-active compound called photoresist. The resistance film isexposed to a light pattern, thereby “exposing” the regions to which thelight is conveyed. However, since topographic features may exist underthe photoresist, it is possible for the light to pass through thephotoresist and reflect off of a topographic feature. This results inresist exposure in an undesirable region. This phenomenon is known as“reflective notching.” As device density increases, reflective notchingbecomes more of a problem.

A similar issue arises as a result of the reflectance normal to theincident angle of irradiation. Such reflectance can create distortionsin the exposure beam through the phenomenon of standing wave formation,thereby resulting in pattern distortion in the photoresist.

In order to combat these phenomena, the use of anti-reflective coatinglayers has become common. The photoresist films are typically depositedeither on top of or below an anti-reflective coating layer. Since boththe photoresist layer and the anti-reflective coating layer are merely“temporary” layers used in intermediate fabrication steps, they must beremoved after such intermediate fabrication steps are completed.

It has been found that the process of FIG. 3 may be used with aprocessing liquid comprised of water and ammonium hydroxide to removeboth the photoresist and the anti-reflective coating in a singleprocessing step (e.g., the steps illustrated at 210-215). Although thishas been demonstrated at concentrations between 0.02% and 0.04% ammoniumhydroxide by weight in water, other concentrations are also consideredto be viable.

The process for concurrently removing photoresist and the correspondinganti-reflective layer is not necessarily restricted to processingliquids that include ammonium hydroxide. Rather, the principal goal ofthe additive is to elevate the pH of the solution that is sprayed ontothe wafer surface. Preferably, the pH should be raised so that it isbetween about 8.5 and 11. Although bases such as sodium hydroxide and/orpotassium hydroxide may be used for such removal, they are deemed to beless desirable due to concerns over mobile ion contamination. However,chemistries such as TMAH (tetra-methyl ammonium hydroxide) are suitableand do not elicit the same a mobile ion contamination concerns. Ionizedwater that is rich in hydroxyl radicals may also be used.

The dilute ammonium hydroxide solution may be applied in the process inany number of manners. For example, syringe pumps, or other precisionchemical applicators, can be used to enable single-use of the solutionstream. In such an embodiment, it becomes possible to strip thephotoresist using a deionized water stream with ozone, and can concludethe strip with a brief period during which ammonium hydroxide isinjected into the aqueous stream. This assists in minimizing chemicalusage and waste generation. The application apparatus may also becapable of monitoring and controlling the pH the using the appropriatesensors and actuators, for example, by use of microprocessor control.

With reference to FIG. 4, there is shown yet a further embodiment of theozone treatment system 227. In the embodiment of FIG. 4, one or morenozzles 230 are disposed within the treatment chamber 15 to conductozone from ozone generator 75 directly into the reaction environment.The heated treatment fluid is provided to the chamber 15 through nozzles40 that receive the treatment fluid, such as heated deionized water,through a supply line that is separate from the ozone supply line. Assuch, injection of ozone in fluid path 60 is optional.

Another embodiment of an ozone treatment system is shown generally at250 in FIG. 5. In the system 250, a steam boiler 260 that suppliessaturated steam under pressure to the process chamber 15 has replacedthe pump mechanism. The reaction chamber 15 is preferably sealed tothereby form a pressurized atmosphere for the reactions. For example,saturated steam at 126 degrees Celsius could be generated by steamboiler 260 and supplied to reaction chamber 15 to generate a pressure of35 psia therein during the workpiece processing. Ozone may be directlyinjected into the chamber 15 as shown, and/or may be injected into thepath 60 for concurrent supply with the steam. Using the systemarchitecture of this embodiment, it is thus possible to achievesemiconductor workpiece surface temperatures in excess of 100 degreesCelsius, thereby further accelerating the reaction kinetics. The steamgenerator in FIG. 5 may be replaced with a heater(s) as shown in FIGS.1-4. While FIGS. 4 and 5 show the fluid and ozone delivered via separatenozzles 40, they may also be, delivered from the same nozzles, usingappropriate valves.

A still further enhancement that may be made to any one of the foregoingsystems is illustrated in FIG. 6. In this embodiment, an ultra-violet orinfrared lamp 300 is used to irradiate the surface of the semiconductorworkpiece 20 during processing. Such irradiation further enhances thereaction kinetics. Although this irradiation technique is applicable tobatch semiconductor workpiece processing, it is more easily andeconomically implemented in the illustrated single wafer processingenvironment where the workpiece is more easily completely exposed to theUV radiation. Megasonic or ultrasonic nozzles 40 may also be used.

With reference to FIG. 7, a further system 310 for implementing one ormore of the foregoing processes is set forth. Of particular note insystem 310 is the use of one or more liquid-gas contactors 315 that areused to promote the dissolution of ozone into the aqueous stream. Suchcontactors are of particular benefit when the temperature of theprocessing liquid is, for example, at or near ambient. Such lowtemperatures may be required to control corrosion that may be promotedon films such as aluminum/silicon/copper.

The contactor 315 is preferably of a parallel counter-flow design inwhich liquid is introduced into one end and the ozone gas is introducedinto the opposite end. Such contactors are available from e.g., W. L.Gore Corporation, Newark, Del., USA. These contactors operate underpressure, typically from about 1 to 4 atmospheres (gauge). Theundissolved gas exiting the contactor 315 may be optionally directed tothe process chamber 320 to minimize gas losses. However, the ozonesupply 330 for the contactor 315 may or may not be the same as thesupply for direct delivery to the process chamber 320.

As described, the ozone gas may be separately sprayed, or otherwiseintroduced as a gas into the process chamber, where it can diffusethrough the liquid boundary layer on the workpiece. The fluid ispreferably heated and sprayed or otherwise applied to the workpiece,without ozone injected into the fluid before the fluid is applied to theworkpiece.

Alternatively, the ozone may be injected into the fluid, and then theozone containing fluid applied to the workpiece. In this embodiment, ifthe fluid is heated, the heating preferably is performed before theozone is injected into the fluid, to reduce the amount of ozonebreakdown in the fluid during the fluid heating. Typically, due to thelarger amounts of ozone desired to be injected into the fluid, and thelow solubility of the ozone gas in the heated fluid, the fluid willcontain some dissolved ozone, and may also contain ozone bubbles.

It is also possible to use aspects of both embodiments, that is tointroduce ozone gas directly into the process chamber, and to alsointroduce ozone into the fluid before the fluid is delivered into theprocess chamber. Thus, various methods may be used for introducing ozoneinto the chamber.

The presently disclosed apparatus and methods may be used to treatworkpieces beyond the semiconductor workpieces described above. Forexample, other workpieces, such as flat panel displays, hard disk media,CD glass, etc, may also have their surfaces treated using the foregoingapparatus and methods.

Although the preferred treatment liquid for the disclosed application isdeionized water, other treatment liquids may also be used. For example,acidic and basic solutions may be used, depending on the particularsurface to be treated and the material that is to be removed. Treatmentliquids comprising sulfuric acid, hydrochloric acid, and ammoniumhydroxide may be useful in various applications.

As described, one aspect of the process is the use of steam (water vaporat temperatures exceeding 100 C) to enhance the strip rate ofphotoresist in the presence of an ozone environment. Preliminary testingshows that a process using hot water at 95 C produces a photoresiststrip rate of around 3000-4000 angstroms per minute. Performing asimilar process using steam at 120-130 C results in a strip rate ofaround 7000-8000 angstroms per minute. However, the resultant strip rateis not sustainable.

The high strip rate is achieved only when the steam condenses on thewafer surface. The wafer temperature rapidly approaches thermalequilibrium with the steam, and as equilibrium is achieved, there is nolonger a thermal gradient to promote the formation of the condensatefilm. This results in the loss of the liquid boundary layer on the wafersurface. The boundary layer appears to be essential to promote theoxidation of the organic materials on the wafer surface. The absence ofthe liquid film results in a significant drop in the strip rate onphotoresist.

Additionally, once the steam ceases to condense on the wafer surface,the reaction environment experiences the elimination of an energy sourceto drive the reaction kinetics. As steam condenses on the wafer surface,it must relinquish the heat of vaporization, which is approximately 540calories per gram. This energy then becomes available to promote otherreactions such as the oxidation of carbon compounds in the presence ofozone or oxygen free radicals.

In view of these experimental observations, a method for maintaining thetemperature of a surface such as a semiconductor wafer surface, isprovided to ensure that condensation from a steam environment continuesindefinitely, thereby enabling the use of steam in applications such asphotoresist strip in the presence of ozone. Thus the formation of theliquid boundary layer is assured, as well as the release of significantamounts of energy as the steam condenses.

To accomplish this, the wafer surface must be maintained at atemperature lower than that of the steam delivered to the processchamber. This may be achieved by attaching the wafer to atemperature-controlled surface or plate 350 which will act as a heatsink. This surface may then be temperature controlled either through theuse of cooling coils, a solid-state heat exchanger, or other means.

In a preferred embodiment, a temperature-controlled stream of liquid isdelivered to the back surface of a wafer, while steam and ozone aredelivered to an enclosed process region and the steam is allowed tocondense on the wafer surface. The wafer may be rotated to promoteuniform distribution of the boundary layer, as well as helping to definethe thickness of the boundary layer through centrifugal force. However,rotation is not an absolute requirement. The cooling stream must be at atemperature lower than the steam. If the cooling stream is water, atemperature of 75 or 85-95 C is preferably used, with steam temperaturesin excess of 100 C.

In another embodiment, and one which is relatively easy to implement ina batch process, pulsed spray of cooling liquid is applied periodicallyto reduce the wafer temperature. Steam delivery may either be continuousor pulsed as well.

The wafer may be in any orientation and additives such as hydrofluoricacid, ammonium hydroxide or some other chemical may be added to thesystem to promote the cleaning of the surface or the removal of specificclasses of materials other than or in addition to organic materials.

This process enables the use of temperatures greater than 100 C topromote reaction kinetics in the water/ozone system for the purpose ofremoving organic or other materials from a surface. It helps ensure thecontinuous formation of a condensate film by preventing the surface fromachieving thermal equilibrium with the steam. It also takes advantage ofthe liberated heat of vaporization in order to promote reaction ratesand potentially allow the removal of more difficult materials which mayrequire more energy than can be readily delivered in a hot waterprocess.

Thus, novel systems and methods have been described. Varioussubstitutions and modifications can of course be made without departingfrom the spirit and scope of the invention. The invention, therefore,should not be restricted, except to the following claims and theirequivalents.

1. An apparatus for processing a workpiece, comprising: a processchamber; a workpiece holder in the process chamber for holding theworkpiece; a steam generator connecting with the process chamber fordelivering steam into the process chamber; an ozone generator connectingwith the process chamber for delivering ozone into the process chamber;and a cooling fluid supply connecting with the process chamber fordelivering a cooling fluid to a second side of the workpiece.
 2. Theapparatus of claim 1 wherein the cooling fluid is provided at atemperature lower than the temperature of the steam.
 3. The apparatus ofclaim 1 wherein the process chamber is sealed to be pressure tight. 4.The apparatus of claim 1 wherein the steam generator is connected to theprocess chamber with a flow line including a filter.
 5. The apparatus ofclaim 1 further comprising a plurality nozzles in the process chamberfor spraying at least one of the steam, the ozone, and the cooling fluidtoward the workpiece.
 6. The apparatus of claim 1 wherein the coolingfluid supply delivers a cooling liquid into the processing chamber as apulsed spray.
 7. The apparatus of claim 1 wherein the steam generatorprovides steam into the process chamber along with at least one of asurfactant, ammonium hydroxide, an acid hydroxide, sulfuric acid,hydrochloric acid, and de-ionized water.
 8. The apparatus of claim 1further comprising a means for controlling a thickness of a layer ofliquid formed on the first side of the workpiece.
 9. The apparatus ofclaim 1 wherein the workpiece holder comprises a rotor which spinswithin the process chamber.
 10. The apparatus of claim 1 wherein thecooling liquid is at a temperature of 75° C. to 95° C.
 11. The apparatusof claim 1 further comprising a steam flow line leading from the steamgenerator into the process chamber, and an ozone flow line leading fromthe ozone generator directly or indirectly into the steam flow line, formixing the ozone with the steam before the ozone and the steam aresupplied into the process chamber.
 12. The apparatus of claim 1 whereinthe workpiece holder holds the workpiece in a vertical orientation. 13.An apparatus for processing a workpiece, comprising: a process chamber;a workpiece holder in the process chamber for holding the workpiece; asteam generator connecting into the process chamber for delivering steaminto the process chamber; an ozone generator connecting into the processchamber for delivering ozone into the process chamber; and a heat sinkin contact with a second side of the workpiece for maintaining theworkpiece at a temperature lower than the temperature of the steam. 14.The apparatus of claim 13 wherein the heat sink comprises a platetemperature-controlled via a cooling coil.
 15. The apparatus of claim 13wherein the heat sink comprises a plate temperature-controlled via aheat exchanger.
 16. The apparatus of claim 13 further comprising meansfor controlling a thickness of a layer of condensate liquid formed onthe first side of the workpiece.
 17. The apparatus of claim 13 whereinthe workpiece holder can be rotated.
 18. The apparatus of claim 13further comprising a steam flow line leading from the steam generatorinto the process chamber, and an ozone flow line leading from the ozonegenerator directly or indirectly into the steam flow line, for mixingthe ozone with the steam before the ozone and the steam are suppliedinto the process chamber.
 19. An apparatus for processing a workpiece,comprising: a process chamber; a workpiece holder in the process chamberfor holding the workpiece; means for delivering steam into the processchamber; means for delivering ozone into the process chamber; and meansfor cooling the workpiece to a temperature lower than a temperature ofthe steam.
 20. The apparatus of claim 19 further comprising means forforming a layer of liquid on the first side of the workpiece, and forcontrolling the thickness of the layer of liquid.
 21. The apparatus ofclaim 19 further comprising chamber heating means for heating thechamber.
 22. The apparatus of claim 19 with the workpiece holder havingmultiple workpiece holding positions.